With the continuing scaling down in real estate for semiconductor device manufacturing, non-planar semiconductor devices are expected to play an ever increasing important role in the areas of field-effect-transistor (FET) beyond certain node size, such as beyond 22 nm node, for at least one simple reason: these devices demand less real estate for manufacturing. There are many different types of non-planar semiconductor devices including for example tri-gate devices, such as tri-gate static-random-access-memory (SRAM), and fin-type FET (FinFET). FinFET transistors may include a p-type dopant doped FinFET (or PFET in short) and an n-type dopant doped FinFET (or NFET in short).
During manufacturing of non-planar devices as well as other types of devices, silicon-based epitaxial film is often used to form access to these devices as a means to lower access resistance. Silicon-based epitaxial film may be used in forming conductive regions as well, where desirable dopants may be incorporated into the epitaxially grown film through, for example, in-situ doping. On the other hand, borderless contacts to the devices may be favored and/or desirable beyond the 22 nm node as overlay tolerances shrink due to continued feature pitch scaling. Silicon-based epitaxial film growth, through forming doped regions, may form a borderless contact to the source and drain of a non-planar FET device.
Generally, silicon-based epitaxial film grows both vertically and laterally on FinFET devices due to the exposed sidewall facet of the fins. For example, for demonstrative purpose, FIGS. 11A-11C are simplified illustrations of perspective, top, and cross-sectional views respectively of a semiconductor structure in a process of manufacturing thereof as is known in the art. More specifically, a plurality of fins such as fins 201, 202, 203, and 204 are formed from a silicon-on-insulator (SOI) substrate 220. During manufacturing, a silicon-based epitaxial film may be formed. Growth of the epitaxial film is selective to silicon material. In other words, the film will grow only on top of silicon material and not on other material such as, for example, silicon-oxide (SiO2) or silicon-nitride (SiN). More specifically, the epitaxial film will not grow on top of oxide layer 200 of SOI substrate 220. The epitaxial film may grow from sidewall surfaces of fins 201-204 and the growth direction may depend upon the exposed facets of the fins. For the example being illustrated in FIG. 11, films 211 and 212 may grow from sidewalls of fin 201; films 213 and 214 may grow from sidewalls of fin 202; films 215 and 216 may grow from sidewalls of fin 203; and films 217 and 218 may grow from sidewalls of fin 204. As is demonstratively illustrated in FIG. 11C, with the lateral epitaxial growth, films 214 and 215, for example, may eventually grow sufficiently big to become in contact with each other, causing shorting of fin 202 with fin 203.
Conventionally, in order to avoid shorting of neighboring fins due to lateral growth of silicon-based epitaxial film, the distance, or pitch, between neighboring fins have to be intentionally increased. However, in high density SRAM cells where spacing between fins of n-type FinFET and p-type FinFET is a dominant factor in determining cell density, the thickness of epitaxial RSD (raised source/drain) may ultimately limit the density of the cell or preclude the use of epitaxial film as a borderless contact.